SUMMARY The long-term goal of my laboratory is to elucidate the mechanisms that control mechanotransduction in hair cells, and the defects in this process that cause deafness. We propose here to study the mechanisms that regulate the assembly and function of the hair cell's mechanotransduction complex. We hypothesize that several proteins including TMIE, LHFPL5, TMC1/2, and CIB2 assemble into a mechanotransduction complex in hair cell stereocilia. We predict that some of these proteins contribute to the pore of the transduction channel while other regulate pore properties or link the channel to the tip link and the cytoskeleton. We also predict that a specialized molecular machinery regulates the transport of the components of the mechanotransduction machinery from the cell body into stereocilia. To test our hypothesis, we will use genetically modified combined with biochemical, cell biological and electrophysiological methods to study protein function in protein transport and mechanotransduction. Our preliminary data show the feasibility of our approach. We have new evidence regarding the mechanisms by which components of the mechanotransduction machinery function within the transduction complex and we have identified new proteins that regulate protein transport from the cell body into stereocilia.